Method of lining internal spiral grooves of a tube with resilient material



G. MlSTlC 3,355,533 METHOD OF LINING INTERNAL SPIRAL GROOVES OF A TUBENov. 28, 1967 WITH RESILIENT MATERIAL 1 Filed June 5, 1964 2Sheets-Sheet 1 GEORGE MISTIC l'll Ill

, 3,355,533 METHOD OF LINING INTERNAL SPIRAL GROOVES OF A TUBE G. MISTICNov. 28, 1967 WITH RESILIENT MATERIAL I 2 Sheets-Sheet 2 Filed June 5,1964 INVENTOR Aflys.

GEORGE MISTIC fir/f N I I\ I I h \I W I \I\ n 2 %M a y z o o o 7/ 6.mwmfimEoo m mm mm\ 7 54 III nmwmmaEoo United States Patent METHQD OFLINING INTERNAL SPIRAL GROOVES OF A TUBE WITH RESILIENT MATERIAL GeorgeMistic, Niles, Ill., assignor to Motorola, Inc., Franklin Park, 111., acorporation of Illinois Filed June 3, 1964, Ser. No. 372,285 3 Claims.(Cl. 264-267) ABSTRACT OF THE DISQLOSURE Core movement in an inductancedevice is restrained by the use of a resilient torque producing materialsubstantially evenly filling a spiral groove in a coil form whichcontains a movable core. A tubular injection tool having an outsidediameter substantially equal to the diameter of the inside wall of thetube and radial holes in the outside surface thereof is placed withinthe tube. Resilient material is applied under a predetermined pressurethrough the radial holes to force the resilient material into thegrooves. The tube may be rotated through a predetermined angle toregulate the distribution of the resilient material of the grooves.

In electronic components such as intermediate frequency transformers andcoils, the inductance may be varied for tuning a circuit to a. desiredcharacteristic such as resonance. The windings of such intermediatefrequency transformers and coils are usually wound around the peripheryof a tubular coil form. A core or slug of permeable material is thenpositioned inside the form and held therein by threads or other means.By moving the coil or slug relative to the coil it is possible to varythe inductance of the coil. In order to prevent changes in the coilparameters after postioning the core, it must remain fixed in positioneven though subject to shock andvibration forces. It is also desirablethat the torque developed to fix the core in position remainsubstantially unchanged throughout repeated positionings of the core.Coil form structures presently used, which provide for sufficient torqueto maintain the core in the proper position relative to the coil, areexpensive to manufacture and do not make use of standard readilyavailable components.

It is therefore an object of this invention to provide a method ofmaking an inductance device using standard readily available coil formsand cores, in which the core will remain in fixed position in the coilform after tuning.

Another object of this invention is to provide a method of making aninductance device having a movable core which may have its positionrepeatedly changed without reducing the torque developed to fix the corein position.

Another object of this invention is to provide a method of making aninductance device having a movable core wherein the torque developed tofix the core in position can be established at an-optimum value.

A feature of this invention is the provision of a method of making aninductance device including a hollow cylindrical tube having a spiralgroove on the inside wall thereof substantially evenly filled with aresilient material and with the wall of the tube between the groovebeing substantially free of the resilient material.

Another feature of this invention is the provision of a method of usingan injection tool, which is inserted into a hollow cylindrical coil formhaving a spiral groove on the inside wall thereof, for substantiallyevenly filling at least a portion of the .groove with a resilientmaterial and wherein the clearance between the surface of the tool andthe inside surface of the coil form is a minimum so that the insidesurface of the coil form between the grooves is substantially free ofthe resilient material.

3,355,533 Patented Nov. 28, 1967 The invention is illustrated in thedrawings wherein:

FIG. 1 is a cross-sectional view of a coil form having a resilientmaterial filling a spiral groove on its inside surface;

FIG. 2 illustrates the method by which the resilient material isdeposited within the groove;

FIG. 3 is a cross-sectional view of a portion of the structure shown inFIG. 2;

FIG. 4 is a cross-sectional view of a nozzle and coil form;

FIG. 5 is a cross-sectional view of the structure of FIG. 4;

FIG. 6 is a cross-sectional view of a coil form having a resilientmaterial filling portions of the groove in the form of bands; and

FIG. 7 is a cross-sectional view of a coil form having a resilientmaterial filling spaced portions of the groove.

In practicing this invention a variable inductance device is providedconsisting of a coil wound on a hollow cylindrical coil form having aspiral groove on the inside surface. Within the coil form is positioneda threaded core whose threads cooperate with the spiral groove so thatthe position of the core relative to the coil may be changed. In orderto prevent undesired movement of the core with respect to the coil,while allowing the core to be smoothly positioned with respect to thecoil when desired, the spiral groove is substantially evenly filled witha resilient material such as silicon rubber while the wall between thegrooves is subtantially free from the resilient material so that thecore does not make frictional contact with the resilient materialoutside of the grooves. The resilient material within the groove iscompressed by the threads of the core to provide an even torque ofsuliicient strength to prevent the forces of shock and vibration frommoving the core relative to the coil form. The resilient material isinjected into the grooves by a tool which is inserted into the coilform. The resilient material is forced through holes in the tool and isevenly distributed in the grooves by rotating the coil form relative tothe tool. By making the clearance between the surface of the tool andthe inside surface of the coil form a minimium, the inside surface ofthe coil form between the grooves is maintained substantially free ofresilient material.

By varying the pressure forcing the resilient material through the holesand/ or keeping the tube stationary relative to the tool, the resilientmaterial can be distributed within spaced portions of the groove.Controlling the portion of the groove filled with the resilient materialcon trols the amount of torque developed to fix the core in position.

FIG. 1 is a cross-sectional view of a coil form 6 having a coil 7 woundon the outer periphery. A spiral groove 10 is cut on the inside surfaceof the coil form. A core 8 having threads 13 is positioned within coilform 6. Threads 13 cooperate with groove 14) so that the core 8 may bepositioned within coil form 6. Core 8 has slots 18 on the end surfacesso that a tool such as a screwdriver may be used to position core 8within coil form 6.

Spiral groove 10 of coil form 6 is substantially evenly filled with aresilient material 11 such as silicon rubber. The spaces 12 betweengrooves 10 are substantially free of resilient material. Threads 13 ofcore 8 compress the resilient material within groove 10 developing africtional torque between the resilient material and the threads. Theresilience of the material in groove 10 acts to maintain an even torqueafter repeated positioniugs of the core. Since the space between thewall 12 of the coil form 6 and Wall 15 of core 8 is substantially freeof resilient material, there is no frictional force developed exceptwhere the threads compress the resilient material within the grooves.

FIG. 2 illustrates the method by which the resilient material isdeposited within the groove of the coil form. Compressed air is appliedto a reducing valve 21 through tube 20. Valve 21 is operated by a footpedal 23 to apply compressed air to container 24. Container 24 is heldin position by a bracket 26. An injection tool 27 is secured to apolyethylene bottle 30 containing the resilient material and locatedwithin container 24. A coil form 28 having a spiral groove on the insidesurface is inserted over injection tool 27 and foot pedal 23 isdepressed. The resilient material within bottle 30 is ejected throughholes 19 in injection tool 27 to susbtantially evenly fill the spiralgroove with the resilient material. Coil form 28 is rotated through apredetermined angle to insure an even coating of the resilient materialand removed from injection tool 27.

FIG. 3 is a cross-sectional view of the container 24 and injection tool27 of FIG. 2. Within container 24 is a polyethylene bottle 32 containingthe resilient material. One end of polyethylene bottle 32 includes apiston 33 which is forced toward the neck 36 of polyethylene bottle 32by the force of compressed air applied to inlet 38. An injection tool 39is secured by threaded means to polyethylene bottle 32. Injection tool39 has a central longitudinal hole 40 and radial holes 41. The resilientmaterial is forced through holes 40 and 41 by the action of piston 33.

An enlarged view of the tool inserted within a coil form is shown inFIGS. 4 and 5. Radial holes 42 connect central longitudinal hole 43 withthe outside surface 44 of tool 46. The diameter of tool 46 issubstantially equal to the inside diameter of coil form 47 so that theclearance between the outside surface of the tool and the inside surfaceof the coil form is as small as possible. The resilient material isforced through center hole 43 and radial holes 42 to substantiallyevenly fill grooves 48 of coil form 47. Coil form 47 is rotated aroundtool 46 as shown in FIG. through an angle at least equal to the anglebetween the rows of radial holes, in this case 120. This insures evendistribution of the resilient material throughout groove 48 of coil form47. By making the clearance 49 between the surface of tool 46 and coilform 47 a minimum the inside surface of coil form 47 between the groovesis substantially free of resilient material. After the grooves have beenfilled, coil form 47 is removed from tool 46.

The amount of torque developed by the resilient material in frictionalcontact with the core can be established at an optimum value bydistributing the resilient material within spaced portions of thegroove. This is accomplished by varying the pressure used to force theresilient material through the holes and/or by keeping the tubestationary relative to the tool. By establishing the air pressureapplied to force the resilient material through the holes at apredetermined value and rotating the tube, the resilient material can bedistributed in the form of bands as shown at 50 in FIG. 6. If the tubeis not rotated with respect to the tool while the resilient material isforced through the holes, spaced arcs of the groove are filled as shownat 52 of FIG. 7.

Thus a simple eifective structure has been shown for providing a torqueto control movement of a core within 4 a coil form. The structure usesstandard readily available coil forms and cores andthe position of thecore can be easily and repeatedly changed without loss of the cockingproperties.

I claim:

1. A method of evenly filling at least a portion of a spiral groove cuton the inside wall of a hollow cylindrical tube with a resilientmaterial while maintaining the inside wall of the tube between saidgrooves substantially free of said resilient material, including thesteps of, placing within said tube a tubular injection tool which has anoutside diameter substantially equal to the diameter of said inside wallof said tube and radial holes in the outside surface thereof, applyingsaid resilient material under a predetermined pressure through saidradial holes whereby said resilient material is forced into at least aportion of said grooves, and withdrawing said tool from said tube.

2. A method of evenly filling a spiral groove cut on the inside wall ofa hollow cylindrical tube with a resilient material while maintainingthe inside wall of the tube between said grooves substantially free ofsaid resilient material, including the steps of, placing within saidtube a tubular injection tool which has an outside diametersubstantially equal to the diameter of said inside wall of said tube andradial holes in the outside surface thereof at a predetermined angularposition, applying said resilient material under pressure through saidradial holes whereby said resilient material is forced into saidgrooves, rotating said tube through an angle at least equal to saidpredetermined angle, and Withdrawing said tool from said tube.

3. A method of evenly filling a spiral groove cut on the inside wall ofa hollow cylindrical tube with a silicon rubber mixture Whilemaintaining the inside wall of the tube between said groovessubstantially free of said silicon rubber, including the steps of,placing within said tube a tubular injection tool which has an outsidediameter substantially equal to the diameter of said inside wall of saidtube and radial holes in the outside surface thereof at predeterminedangular position, applying said silicon rubber under pressure throughsaid radial holes whereby said silicon rubber is forced into saidgrooves, rotating said tube through an angle at least equal to saidpredetermined angle, and withdrawing said tool from said tube.

References Cited UNITED STATES PATENTS ROBERT F. WHITE, PrimaryExaminer.

T. J. CARVIS, Assistant Examiner,

1. A METHOD OF EVENLY FILLING AT LEAST A PORTION OF A SPIRAL GROOVE CUTON THE INSIDE WALL OF A HOLLOW CYLINDRICAL TUBE WITH A RESILIENTMATERIAL WHILE MAINTAINING THE INSIDE WALL OF THE TUBE BETWEEN SAIDGROOVES SUBSTANTIALLY FREE OF SAID RESILIENT MATERIAL, INCLUDING THESTEPS OF, PLACING WITHIN SAID TUBE A TUBULAR INJECTION TOOL WHICH HAS ANOUTSIDE DIAMETER SUBSTANTIALLY EQUAL TO THE DIAMETER OF SAID INSIDE WALLOF SAID TUBE AND RADIAL HOLES IN THE OUTSIDE SURFACE THREOF, APPLYINGSAID RESILIENT MATERIAL UNDER A PREDETERMINED PRESSURE THROUGH SAIDRADIAL HOLES WHEREBY SAID RESILIENT MATERIAL IS FORCED INTO AT LEAST APORTION OF SAID GROOVES, AND WITHDRAWING SAID TOOL FROM SAID TUBE.